In recent years Low-Density Parity-Check (LDPC) codes [1] have gained attention with their capability to achieve near Shannon limit performance. Although LDPC codes of random construction allow for a high degree of parallelism, the randomness of the parity-check matrix makes it difficult to exploit in hardware. This disadvantage has lead to several approaches of designing structured irregular LDPC codes [2, 3], that are suitable for an efficient hardware implementation, yielding very high throughput. They are designed using different methods, but the basic idea is to partition the parity-check matrix into non-overlapping block rows and block columns. One such approach is to use a permutation matrix. Under this design method, one belief propagation algorithm [4] has been proposed, where an LDPC decoding iteration is broken into sub-iterations. During each sub-iteration updated log-likelihood ratios (LLRs) are computed for each of the non-overlapping block rows.
It is shown for single-carrier systems in [5] that an iterative minimum-mean square error (MMSE) equalizer combined with soft data detector lead to both better channel estimation and BER performance. Thus, iterative estimation/detection structures based on these latter methods may also yield better BER performance in OFDM systems with unknown channels.
In the conventional RLS channel estimator, the hard decision from the data detector is used. Also, only one shot by the detector-channel estimator-decoder chain is used.
FIG. 1 herein, which reproduces FIG. 3 of Lu et al., “Performance Analysis and Design Optimization of LDPC-Coded MIMO OFDM Systems”, IEEE Transactions on Signal Processing, Vol. 52, No. 2, February 2004, pps. 348-361, which was attached as Exhibit K to the above-referenced US Provisional Application and incorporated by reference therein its entirety, is illustrative of a conventional Turbo receiver structure that employs a soft demodulator and a soft LDPC decoder for an LDPC-coded Multiple-Input, Multiple Output (MIMO) Orthogonal Frequency Division Multiplex (OFDM) system.